1. Field of the Invention
The invention concerns a device for the separation of flat elements, such as for instance blanked discs, to be lifted one at a time and removed for subsequent operations.
2. Description of Related Art
Some separating devices are known, which are connected with lifting devices acting on flat elements stacked in piles on an underlying storage surface. The simplest lifting devices foresee an element of contact with the piece to be lifted, which acts with a pre-determined and adjustable force. For instance, in the case of non-stainless steel sheets the pre-determined lifting force consists of a suitably dimensioned magnet, inserted in the mechanical lifting arm. On the other hand, in the case of non-magnetic materials, such as stainless steel or brass, the drawing is done by means of a sucker acting by depression. In this case too, by varying the vacuum percentage within the sucker, the lifting force can be increased and gauged to lift pre-determined weights.
It is obvious that, as soon as the adhesion conditions between one flat element and the next one in the pile to be drawn from vary, the efforts necessary to separate and lift each individual element from the others change. This happens for instance when the oil left from preceding operations dries up and acts as an actual adhesive between one metal sheet and the next. Other variable elements are rust or even the blanking burrs.
All these elements contribute to making extremely variable the effort necessary for the sucker or the magnet to separate and lift a single piece. Thus it happens that, since the lifting strength exerted by the sucker or the magnet must necessarily be higher than the weight of one piece, very often two pieces, rather than one, are lifted at the same time. If two pieces are lifted together and put inadvertently under a blanking or drawing die, the die may break and/or the presses carrying the die may undergo serious damage.
For this reason the known technique has striven to achieve a certain degree of certainty in the lifting of each single piece by performing, for instance, an exfoliation of the pieces stacked in a pile beforehand, the pile presenting toothed bars arranged on diameters which are smaller than the diameters of the pieces, so that the pieces themselves, usually in the shape of discs, separate from each other.
This system yields satisfactory results for some types of metal sheets, but it finds its limit of application when the thickness of the metal sheet exceeds 6-7 tenths of a millimeter and its diameter is larger than 300-350 mm. In fact, when these limits are exceeded, the exfoliation of the metal sheets by bending is no longer practical because of the metal sheet resistance. Other methods of separation exist, based for instance on the vibration of the entire pile, but they also present a considerable degree of uncertainty, as well as of complexity.